Reed switch

ABSTRACT

A reed switch comprises a pair of reeds positioned so that the locus of operation of the free end of at least one of the reeds does not cross the other of the reeds. Contact material is provided in the area of the free end of each of the reeds. The contact material on at least one of the reeds is mounted to deviate from the free end of the one of the reeds.

,Ullitd States Patent 91 I45] Feb.'l3,'1973 Hara et al.

v [s41 REED SWITCH" [75] Inventors: 'Toshito l-la'i'a', Kawasaki;Toshiro Oguma, Suzaka-shiQ Nagano-ken, I

1 v 6' Attorney-Arthur E. wilfond etal.

p n both of Japan [731 Assignee': Fujitsu Limited, Kawasaki, Japan 221Filed:; uses/1971 21 Appl. No.: 206,013

[30] Foreign ApplicationlriorityData a Dec.l l,l9 70 Japan ..4s/|0939s,

52' User. .L ..-;..33s/1s4 [51] lnt.Cl. ....ll0lh'5l/28 [58]" FieldofSeareh..... ..j......,. ....335/151-154 1 References Cited 7 UNl'lEDsTA'TEs PATENiS v 3,321,263 6/1967 Korn ..335/|54 2,892,052 6/1959Ducati..... .335/154 Primary Examiner-Roy N. Envall, Jr.

[57] ABSTRACT A reed switch comprises apair of reeds positioned so thatthe locus of operation of the freeend of at least one of the reeds doesnot cross the other of the reeds. Contact material is provided in thearea of the free I end of each of the reeds. The contact material on atleast one of the reeds is mounted to deviate from the free end of theone of thereeds.

9 Claims, 13 Drawing Figures v PATENTED FEB 1 3191s SHEET 2 BF 3 Sol 8098 803 8 v i 02 L Z \l/ W i W V FIG; 8d

\A Mf \I} PAIEIIIEII E I 3,716,810

SHEET 3 OF 3 Fl G 50 MAGNETIC I 'FLUX DENSITY D I 30 ExcITATloN 1NAMPERE-TURNS ATTRACTIVE F RCE N GRAMS o'.I 62 d3 REED DISPLACEMENT IN MMampere -turnseand, the

REED swncir The present invention relates to-a reed switch. Moreparticularly,theinvention relates, to areed switch used to close andopen. an electri'c circuit.

The reed switch of the, invention comprisesa pair of.

reeds of ferromagnetic material positioned in a manner whereby thelo'ctts of operation of the free end of at least one 'of thereedscannotcross. the other reed. .The

as, foreiiample, nitrogen, therein. The reed, switch is positioned in aJOiLtb providefa reed relay.

A, defect of a known type of reed. switch. is that; the

- reeds are sealed in a glasstubeihaving an inert gas such materialoffthe, contacts gnd. the method of manufacture ofthecotitactsjareextremely limited. The life of the reeds witchisshorteneddueto this defe,c t, because- :the contact gap cannot be madelargeenough and the thicknessof thecontacts, cannot.

bemadelarge except in a large-size switch; 1. I

Another defect of known types of reed, switch is-the very short slidingat the contact. Still,,anotherdefect of known types of reednsvwitchisthat, in order. to protect the contact fromadhesionby melting, aprotective-circuit is required, sincethe releaseis non-abruptand has aweak initialor opening force. Another defect of knowntypeset":reedswitch ,isvthatptheyfcannot be utilized; as a th'reshold;"mitt-element,lbecause'the. working releaseampere-turns are different. i

The principalobjefct of theyinventionn is:- toprovide a new. and,improved Freed; .switchiwhi'ch overcomes th disadvantagesofknowniypesofi reed-switch- An object; of.- thein vention= isto providea-ireedswitch having along,lif,e j I Anothenobjecoof the-invention;isttoprovidezareed switchihaving longslidingflat;theacontactt Still another;object. of, the. invention is.t,0, provide a reed:switch.in,whichhthereisno danger of adhesion of the. contactsandg. therejs. n0,Protectivecircuit utilized to prevent such; adhesion-1 Another.objectof the-invention is,,to p'rovide a reed switch which may -.beutilizedas a.;threshold limit element. s iAnotherobjectlof theinventionistoprovide a reed switchhavinga largecontactfgap; thick contacts andlong slidingjatthe. contacts, which: reed. switch is par- Iticularlysuitablefor useg-in telecommunication equipment, telephoneexchangeequjpmentand.various electronicv equipment andlfunctions;therein with long life, high reliability, efficiencyand,effectiveness.

"Yet another:object 'ofi the invention istoprovide a reedswitch having;impulsiverelease-pf the contacts.

Another object. of-the,inivention isato.provide. a, reed switch, havingthesam'eworkingv ampere-turns and releasing ampere turns, so. thatit-.is-.utili'zable asareed relay and asathresholdlimitelement.

In accordance with the/invention,areed switchcomprises-a,pair-of;reeds.:positionedfl-so that'the locus of operationof; the, free-,end of at1least -one of the .reeds does not cross,theothenofathe reeds. Contact material is, provided in -the area. of the,ireeaendof each of the reeds. The contact-material.on.:at leastpone ofthe reeds is mountedgto .deviatefromthe' free .;end .;of the one of thereeds. I

The reedsicomprise.ferromagnetic,material."The free ends ofthereedsiar'e spaced from each other in every one of the reeds extendsbeyondthefre'e end of the one of-the reeds toward the other of thereeds. The contact material on the one of the reeds comprises a spring.

The contact material on the one of the reeds may extend substantiallylinearly beyond the free end of the oneof the reeds. The contactmaterial on the one of the reeds may be bent away from thecontactmaterial on the other of the reeds but extends substantially linearlyFIG. 3 is a graphicalprese'ntation of the magneticf characteristics of areed switch of the prioraart;

FIG. .4 is a perspective view of the contact area of an embodiment ofthe reed switch of the invention;-

FIG. 5a is a schematic diagram of the-contact area of another embodimentof the reed'switch of the invention; l

FIG. 5b is aschematic diagram of thecontact area of still anotherembodiment of the reed switch of themvention; l

FIG. 6 isa graphical presentationof the magnetic characteristics of thereed" switch of the invention;

FIGKI is a graphical presentation of the magnetic characteristics ofreed switches of the priorart andthe reed switch of the invention; and."a

' FIGS 8a, '8b,-8c,-8d and 8e are perspective views ofdifferentsmodifications of yet another embodiment of the reed switchofthe invention.

FIG. 1 illustrates a known type. of reed switch: In FIG. 1, reeds 1'and-2 are of rod-like configuration and comprise, for example, 52 alloy.g

The free ends of the .reeds land 2, which are to bear the'contactmaterial, are melted down in order to provide them with an appropriatespring or resiliency characteristic. The free. end 3 of the: reed-1' isplated with the contact'material. The free end 4of the reed 2 is platedwith thecontactmaterial. The contact material comprises precious metals.

The reeds 1 and 2 are sealed in a glass tube 51in the.

area of .their contacts 3-and4 in order to prevent oxidation ofsaidcontacts. The reedswitch may be inserted 7 into a coil or winding6whichrnay be woundon a bob condition'ofthe, switch-and-the contactmaterial on the bin 7, thereby providing a reed relay.

When the-coil-6 i'senergized, the reeds1 and2 are magnetized and theircontacts 3 and 4 move under the influence of the attractivev magneticforce into contact with each'other.

F IG. 2 illustrates the area'of the contacts of a known type-ofreedswitch. FIG. 2'isa representation of the contact area of the reedswitch of FIG. 1 on a considerably enlarged scale. In FIG. 2, the area8is the melted down partofthereed'l andthe area 9 is the melted downpartof the reed 2.; The reedl has a contact part 11, which'is the freeend of said reed, plated v with precious metals. The reed 2 has acontact part-12', which-is the free endof said'reed; platedwithpreciousmetals. 1

in section, of 'a'reed'switch of I l The contact areas 11 and 12 arepositioned adjacent each other in a manner whereby the locus ofoperation of each crosses the other. The contacts 11 and 12 are spacedfrom each other by a distance x,. The force of 'magnetic attraction onthe reeds l and 2 in their contact areas 11 and 12 is directlyproportional to the gap or space '16,. The space x, may thus not beincreased since a large attractive force is required.

In a. usual small-sized reed switch the distance .1: is from 50 to 120microns. For this reason, it is impossible to cover the contact areas 11and 12 with thick nonmagnetic material'to provide bulk'contacts. Thecontact areas are usually formed 'by thin non-magnetic material appliedby plating or sputtering. The contact material is thus very restricted.Since the contacts 11 and 12 are thin, they suffer erosion, transfer andwear due to the impact ,of said contacts and the current flowing betweensaid contacts at the instant of make and break after a specific numberof operations. This results in bad contact or improper release.Furthermore, uneve'ness in the contacts due to the transfer is increasedin accordance with the'magnitude of the current'flowing between saidcontacts.

Improper-release may be caused b'y'minute-unevenness in aknown reedrelay in which the gap x, between the contacts cannot be made large.Furthermore, it is obvious that make and break of the large currentwhich increases unevenness due to the transfer becomes impossiblenln aconventional reed relay the release is non-abrupt in the structure ofFIG. 1, so that improper release is inevitable. v I

FIG. 3 illustrates the magnetic characteristic of a known reed switch.In FIG. 3, the abscissa represents the excitation in ampere-turns and.the ordinate represents the magnetic flux density dz. As shown in FIG.3, working ampere-turns are illustrated at a point m and the releaseampere-turns are illustrated at a point n. The release ampere-turns areless than the working ampere-'tums. This is due to the magnitude ofthe'demagnetizingfield. That is, the magnitude of the demagnetizingfield is proportional to its length, provided that the material andcross-sectional area are the same. f

When the contacts are released, the produced demagnetizing field isdetermined by the length of each reed, whereas when thecontacts areclosed or in contact, the produced demagnetizing field is determined bythe sum of the length of each reed. Accordingly, the

' magnetic-flux density effectively operating between the contacts isdifferent when the contacts are released and when the contacts areclosed. Thus, the point m of the working ampere-tu'rns and the point nof the release ampere-turns are different. The conventional reed switch,in which the points m and n are different, thus cannot be utilized asthe threshold limit element.

I The defects and disadvantages of known reed switches are eliminated bythe reed switch of the present invention. FIG. 4shows a reed switch ofthe invention. In FIG. 4, the structure of the reed switch is the sameas that of the known reed switch, except that the free endsof the reedsare spaced from each other and the free end of one of the reeds isextended in a direction toward the other. The free ends of a first reed41 and a second reed 42are spaced from each other by and 42 thus doesnot come into contact with that of the other in any condition of theswitch. The reeds 41 and 42 comprise magnetic material.

A contact 43 is provided in the area of the free end of the first reed41. A contact 44 is provided in the area of the free end of the secondreed 42. The contacts may be affixed to the corresponding reeds by anysuitable means such as, for example; welding. The contact 44 of the reed42 extends beyond-the free end of said reed toward the reed 41. When thecontacts 43 and 44 are closed or in contact due to a magnetic biasingfield, the free ends of the reeds 41 and 42 are opposite each other andthe magnetic force of attraction produced by the magnetic gradient isutilized as the contact force between said contacts. The reeds 41 and 42comprise magnetic material such as, for example, 52 alloy. The contacts43 and 44 comprise materials such as, for example, nickel, tungsten,molybdenum, lead, gold and silver, and palladium and mercury.

vThe thickness of the contact 44 is selected for suitable or appropriatestiffness so that said contact functions as a spring or resilient body.Since the free ends of the reeds 41 and 42 do not overlap, the gap xbetween the contacts 43 and 44 thereof may be made large. The bottomsurfaceof the reed 42 is spaced a distance x;, from the bottom surfaceof the reed 41.v

The reed switch of the present invention functions in the followingmanner. When the reeds 41 and 42 are magnetized by an exciting magneticfield, the contact 44 of the reed 42 abruptly approaches the contact 43of the reed 41 and said'contacts come into contact with each other. Themovement of the contacts 43 and 44 in a distance or gap t. The free endof each of the reeds 41 I The release force operates as the contactforce between the contacts 43 and 44. The total release force is the sumof the release force based upon the displacement of the reeds 41 and 42and the release force of the contact 44. Stabilization may be providedat the point where the total release force and the attractive force ofthe reeds 41 and 42 come to a balance. These are primarily the verticalcomponents of such forces. The point of balance is a point at which thereeds 41 and 42 slip slightly up and down. That is, the balance ismaintained under a magnetically biased condition.

After the contact 44 contacts the contact 43, the contact 44 is bent sothat the contacts 44 and 43 slide in a linear distance shortened by thebending of the contact 44. Unevenness resulting from the transfer of thecontacts 43 and 44 is scraped or removed by the sliding of said contactsand is accordingly flattened. This results in an improvement of improperrelease due to the transfer. Thus, the reed switch of the inventionpermits a greater make and break of the current than that ofa'conventional reed switch by making the contact gap at, the same as thecontact gap x of the conventional reed switch.

FIG. 6 illustrates the magnetic characteristic of the reed switch of theinvention. In FIG. 6, the abscissa represents the excitationinampere-turns and the ordinate represents the magnetic flux density (b. Apoint P in FIG.'6 represents the working ampere-turns and the releasingampere-turns, which are equal to each other.

The working and releasing ampere-turns are equal, because of thedifference of thereed switch of the invention over a conventional reedswitch, which difference is that there is no contact between the reedsopposite each other and the magnitude of demagnetization is constantindependent of the release and closing of the contact. Accordingly, thereed switch of the invention may be utilized as a threshold limitelement, thereby expanding the utilization of the reed switch.

The speed of release of the contacts 43 and 44 of the reed switch ofFIG. 4, after the release of the bent contact 44, is great comparedtothe speed of .release of the contacts of a conventional reed switch,as shown in FIG. 2, for example. Thisis due to the addition of therelease energy of the contact member 44 in the reed switch of FIG. 4.Thus, the reed switch of the invention provides impulsive release. Sincethe reed switch of the invention provides impulsive release, the forceof contact and the force of release between the contacts are great, sothat adhesion or sticking of the contacts is eliminated.

FIG. 7 illustrates theattractive force characteristics and explains thecontact gap. In FIG. 7, the abscissa represents the displacement of thereed in millimeters and the ordinate represents the attractive force ingrams. In the conventional reed switch 'of FIG. 2, x, is thedisplacement of the reeds l and 2. In the reed switch of the invention,as shown in FIG. 4, the reeds 41 and 42 are displaced by the distancex;,. The distance x is substantially vertical, extending up and down.

In FIG. 7, a curve 7lshows the attractive force characteristic of theconventional reed switch. A curve 72 shows the attractive forcecharacteristic of the reed switch of the invention.In both cases, thereeds comprise a square bar of 52 alloy having'a cross-sectional area of0.37 mm. The thickness of the bar was 0.54 mm and the width of the barwas 0.82 mm. The gap t in the reed switch of the invention, as shown inFIG. 4, was 0.01 mm.

A curve 711 of FIG. 7 shows the release force I characteristic of theconventional reed switch. A curve 721 shows the release forcecharacteristic of the reed grams attractive force. If the attractiveforce charac-.

teristic 71 is selected in-anticipation' of a small surplus, the gap x,between the reeds l and 2 is approximately 0.15 mm. i

In accordance with the invention, however, the release forcecharacteristic shown by the curve 721 of FIG. 7 may be selected towardthe same release force of 5 grams,in which case the displacement xbetween the reeds 41 and 42 (FIG. 4) is approximately 0.34 mm. Ashereinbefore'described, the displacement of thereed switch of theinvention is more than double the displacement of :the conventional readswitch, so that the contactgap is greatly improved.

FIGS. andSbshow another embodiment of the reed switchiof the invention.In each of FIGS. 5a and 5b, the .reeds 51 and 52"c'omprisemagneticmaterial such as, for example, 52 alloy. In each of FIGS. 5a and5b, a contact 53 or 53 is affixed to the reed 51 and a spring 54 or 54'extends from the reed 52 toward the reed 51. A contact 55 or 55' isaffixed to the spring 54 or 54' in each of FIGS. 5a and 5b.

In the embodiment of FIG. 5a, the contacts 53 and 55 are thin and thereis a sufficient contact gap between them. The contact gap may, however,become insufficient due to the necessity for using-thick contacts underthe particular circumstances which determine the use of the reed switch.Thus, for example, the thick contacts 53' and 55' of FIG. 5b may beutilized. In such a case, the desired contact gap may be provided bybending the spring 54' away from the contact 53 but extending saidspring substantially linearly over the- In FIGS. 8a and 8b, the reeds801 and 802 are rods of magnetic material such as, for example, 52alloy. The

area of the free end of the reed 802 is pressed to provide asubstantially plate-like portion 804. A substantially spherical contact805 is affixed to the first read 801 by anysuitable means such as, forexample, welding.

A contact 806 is affixed to the substantially flat portion 804 of thesecond reed 802 at an end 807 thereof.

The contact 806 is resilient and functions as a spring. The contact 806comprises a precious metaLsuch as, for example, tungsten,-nickel;molybdenum, gold and silver, gold and lead, palladium, silver andpalladium, and copper and palladium. The contact 805 comprises aprecious metal of the same group of metals as the contact 806. I 1

In the embodiment of FIG. 8c, the first reed 801 comprises a tube havingan axial bore extending therethrough, instead of a rod, as in theembodiments of FIGS. 8a and 8b. The first reed 801 of FIG. 8c may thusbe utilized for replacing inert gas of nitrogen and hydrogen, orreducing gas such as hydrogen and carbon monoxide, for the air in theglass housing 803 after said housing is sealed. That is, an inert orreducing gas is supplied'through the axial bore of the reed 801. Afterthe gas exchange is completed,the bore of the reed'80l is sealed by anysuitable-means such as, for example,

' welding.

In the embodiments of FIGS. 8d and 8c, the first and second reeds 801'.and 802 have the configuration of plates. In each of FIGS. 8d and 8e,the first and second reeds comprise 52 alloy. The free end of thesecond.

is affixed to said reed by any suitable means such as, for

example, welding, and may have a cylindrical configuration. i

The difference between the embodiments of FIGS. I 8d and 8e is'that inFIG. 8d, a slot 811 is provided in the free end of the contact area 808'to form twin contact parts 812 and 813. This results in more reliablecontact between the contact area 808 and the contact 809. Moreparticularly, one of the contact parts 812 and 813 such as, for example,the contact part 813, has an oxide film. Furthermore, if there is aprojection at the contact 809 which contacts the oxide film, the contactpart 813 is bent. In this case, the other contact part 812 contacts thecontact 809 and results in reliable contact and switching.

Although the embodiments of the invention have been described withreference to reed switches, the magnetic attraction structure of theinvention is applicable to general electromagnetic switches.Furthermore, the aforedescribed embodiments relate to a reed switchhaving a make contact. The invention, however, is applicable to'a reedswitch having a break contact by means of a simple well known technique.

While the invention has been described by means of specific examples andin specific embodiments, it should not be limited thereto, for obviousmodifications will occur to those skilled in the art without departingfrom the spirit and scope of the invention.

We claim:

1. A reed switch comprising a pair of reeds of ferromagnetic material,at least one of said reeds being movable, said reeds having free endsspaced from one another in every condition of the switch, a firstcontact member secured to one of said reeds and passing beyond the freeend if said one reed to extend over the free end of the other reed, anda second contact member secured to said other reed, said switch beingopened and closed at said contact members by the displacement of atleast one of said reeds.

2. A reed switch as claimed in claim 1 wherein said first contact membercomprises a spring.

3. A reed switch as claimed in claim 2 wherein said spring is flexedwhen said contact members are closed during operation of the switch.

4. A reed switch as claimed in claim 1 wherein said first contact membercomprises a resilient plate-like member having one end portion securedto said one reed, said resilient plate-like member normally beingdisposed in a fixed position relative to said one reed except when saidcontact members are mated during operation of the switch, whereupon saidresilient platelike member is flexed by virtue of the mating contact toapply a resilient force between said contact members, said resilientforce being derived from the resiliency of said plate-like member. I

5. A reed switch as claimed in claim 1 wherein said second contactmember is secured to said other reed at a position displaced from thefree end of said other reed.

6. A reed switch as claimed in claim 1 wherein said first contact memberextends substantially linearly beyond the free end of said one reed.

7. A reed switch as claimed in claim 6 wherein said first contact memberis a flat plate.

8. A reed switch as claimed in claim 1 wherein said first contact memberis .bent away from said second contact member but extends substantiallylinearly over said second contact member.

9. A reed switch as claimed in claim 1 wherein at least one of saidreedscomprises a hollow tube.

t III

1. A reed switch comprising a pair of reeds of ferromagnetic material,at least one of said reeds being movable, said reeds having free endsspaced from one another in every condition of the switch, a firstcontact member secured to one of said reeds and passing beyond the freeend if said one reed to extend over the free end of the other reed, anda second contact member secured to said other reed, said switch beingopened and closed at said contact members by the displacement of atleast one of said reeds.
 1. A reed switch comprising a pair of reeds offerromagnetic material, at least one of said reeds being movable, saidreeds having free ends spaced from one another in every condition of theswitch, a first contact member secured to one of said reeds and passingbeyond the free end if said one reed to extend over the free end of theother reed, and a second contact member secured to said other reed, saidswitch being opened and closed at said contact members by thedisplacement of at least one of said reeds.
 2. A reed switch as claimedin claim 1 wherein said first contact member comprises a spring.
 3. Areed switch as claimed in claim 2 wherein said spring is flexed whensaid contact members are closed during operation of the switch.
 4. Areed switch as claimed in cLaim 1 wherein said first contact membercomprises a resilient plate-like member having one end portion securedto said one reed, said resilient plate-like member normally beingdisposed in a fixed position relative to said one reed except when saidcontact members are mated during operation of the switch, whereupon saidresilient plate-like member is flexed by virtue of the mating contact toapply a resilient force between said contact members, said resilientforce being derived from the resiliency of said plate-like member.
 5. Areed switch as claimed in claim 1 wherein said second contact member issecured to said other reed at a position displaced from the free end ofsaid other reed.
 6. A reed switch as claimed in claim 1 wherein saidfirst contact member extends substantially linearly beyond the free endof said one reed.
 7. A reed switch as claimed in claim 6 wherein saidfirst contact member is a flat plate.
 8. A reed switch as claimed inclaim 1 wherein said first contact member is bent away from said secondcontact member but extends substantially linearly over said secondcontact member.